<style>
    * {margin: 0;padding: 0;}
    ul, ol, li {
        list-style: none;
    }
    .box {
        width: 600px;
        height: 400px;
        border: 10px solid #333;
        margin: 30px auto; 
        display: flex;
        flex-direction: column;
    }
    .box > ul {
        width: 100%;  
        height: 40px;
        display: flex; 
    }
    .box > ul > li {
        flex: 1;
        display: flex;
        justify-content: center;
        align-items: center;
        font-size: 30px;
        color: #fff;
        background-color: hotpink;
    }
    .box > ul > li.active {
        background-color: orange;
    }
    .box > ol {
        flex: 1;
        position: relative;
    }
    .box > ol > li {
        width: 100%;
        height: 100%;
        position: absolute;
        top: 0;
        left: 0;
        background-color: skyblue;
        color: #fff;
        font-size: 100px;
        display: flex;
        justify-content: center;
        align-items: center;
        display: none;
    }
    .box > ol > li.active {
        display: flex;
        }
</style>

<div class="box tab1">
    <ul>
        <li class="active">1</li>
        <li>2</li>
        <li>3</li>
    </ul>
    <ol>
        <li class="active">1</li>
        <li>2</li>
        <li>3</li>
    </ol>
</div>
<script src="./demo.js"></script>
<script>
    let obj1 = new Tab('.tab1')
</script>
